The speaker is telling someone how completely she loves them. She begins with a stark image: even if this person were a leper, covered in wounds and rejected by everyone, she would still stand beside them. That exile would not be a burden to her—it would feel like an honor. The first stanza is about loyalty that doesn’t depend on status or acceptance.
The second stanza shifts from hypothetical suffering to pure admiration. This person is not just someone she loves; they are her sun, moon, and starlight—the entire cosmos of her inner life. They are the recurring melody in her heart, the force that gives her direction and purpose. The mood is intense and almost worshipful, but also tender, because this devotion is stated as a simple, undeniable fact.